Rising Scores on Intelligence Tests

This article originally appeared in the September-October 1997 issue of American Scientist.

Average scores on intelligence tests are rising substantially and consistently, all over the world. These gains have been going on for the better part of a century—essentially ever since tests were invented. The rate of gain on standard broad-spectrum IQ tests amounts to three IQ points per decade, and it is even higher on certain specialized measures. In the Netherlands, for example, all male 18-year-olds take a test of abstract-reasoning ability as part of a military-induction requirement. Because the same test is used every year, it is easy to see the mean score rising, in this case, at about seven points per decade.

The cause of these enormous gains remains unknown. At this point, no one even knows whether they reflect genuine increases in intelligence or just the gradual spread of some specialized knack for taking tests. Greater sophistication about tests surely plays some role in the rise, but there are other possible contributing factors: better nutrition, more schooling, altered child-rearing practices and the technology-driven changes of culture itself. Right now, none of these factors can be ruled out; all of them may be playing some part in the increasing scores. Whatever the causes may be, the sheer size of the gains forces us to reconsider many long-held assumptions about intelligence tests and what they measure.

To focus on standardized tests—as this article does—is not to suggest that they measure every form of intelligence. Indeed, they surely do not. Supporters and opponents of testing are often at odds, but no serious scholar claims either that IQ tests measure nothing important or that they measure everything important. At the very least, they do tap certain abilities that are relevant to success in school and do so with remarkable consistency. On the other hand, many significant cognitive traits—creativity, wisdom, practical sense, social sensitivity—are obviously beyond their reach. Because there are no established measures of these subtler traits, no one knows if they are changing too. Standardized-test scores are all that we have, and they are certainly going up. This article will explore the paradoxes created by that rise and the factors that may be responsible for it.